[dev.link] cmd/link: create loader-specific version of GCProg

Create a new version of the GCProg type + methods that use loader APIs
instead of sym.Symbol.

This code isn't actually used just yet, but will be needed once the
wavefront reaches dodata() and we need to convert that phase.

Change-Id: I087521832015818204fe5c2ac99c7bd3f61b2bf0
Reviewed-on: https://go-review.googlesource.com/c/go/+/229037
Run-TryBot: Than McIntosh <thanm@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Cherry Zhang <cherryyz@google.com>

src/cmd/link/internal/ld/data.go

@@ -1257,6 +1257,81 @@ func (p *GCProg) AddSym(s *sym.Symbol) {
 	p.w.Append(prog[4:], nptr)
 }
 
+type GCProg2 struct {
+	ctxt *Link
+	sym  *loader.SymbolBuilder
+	w    gcprog.Writer
+}
+
+func (p *GCProg2) Init(ctxt *Link, name string) {
+	p.ctxt = ctxt
+	symIdx := ctxt.loader.LookupOrCreateSym(name, 0)
+	p.sym = ctxt.loader.MakeSymbolUpdater(symIdx)
+	p.w.Init(p.writeByte())
+	if debugGCProg {
+		fmt.Fprintf(os.Stderr, "ld: start GCProg %s\n", name)
+		p.w.Debug(os.Stderr)
+	}
+}
+
+func (p *GCProg2) writeByte() func(x byte) {
+	return func(x byte) {
+		p.sym.AddUint8(x)
+	}
+}
+
+func (p *GCProg2) End(size int64) {
+	p.w.ZeroUntil(size / int64(p.ctxt.Arch.PtrSize))
+	p.w.End()
+	if debugGCProg {
+		fmt.Fprintf(os.Stderr, "ld: end GCProg\n")
+	}
+}
+
+func (p *GCProg2) AddSym(s loader.Sym) {
+	ldr := p.ctxt.loader
+	typ := ldr.SymGoType(s)
+
+	// Things without pointers should be in sym.SNOPTRDATA or sym.SNOPTRBSS;
+	// everything we see should have pointers and should therefore have a type.
+	if typ == 0 {
+		switch p.sym.Name() {
+		case "runtime.data", "runtime.edata", "runtime.bss", "runtime.ebss":
+			// Ignore special symbols that are sometimes laid out
+			// as real symbols. See comment about dyld on darwin in
+			// the address function.
+			return
+		}
+		p.ctxt.Errorf(p.sym.Sym(), "missing Go type information for global symbol: size %d", ldr.SymSize(s))
+		return
+	}
+
+	ptrsize := int64(p.ctxt.Arch.PtrSize)
+	typData := ldr.Data(typ)
+	nptr := decodetypePtrdata(p.ctxt.Arch, typData) / ptrsize
+
+	if debugGCProg {
+		fmt.Fprintf(os.Stderr, "gcprog sym: %s at %d (ptr=%d+%d)\n", ldr.SymName(s), ldr.SymValue(s), ldr.SymValue(s)/ptrsize, nptr)
+	}
+
+	sval := ldr.SymValue(s)
+	if decodetypeUsegcprog(p.ctxt.Arch, typData) == 0 {
+		// Copy pointers from mask into program.
+		mask := decodetypeGcmask2(p.ctxt, typ)
+		for i := int64(0); i < nptr; i++ {
+			if (mask[i/8]>>uint(i%8))&1 != 0 {
+				p.w.Ptr(sval/ptrsize + i)
+			}
+		}
+		return
+	}
+
+	// Copy program.
+	prog := decodetypeGcprog2(p.ctxt, typ)
+	p.w.ZeroUntil(sval / ptrsize)
+	p.w.Append(prog[4:], nptr)
+}
+
 // dataSortKey is used to sort a slice of data symbol *sym.Symbol pointers.
 // The sort keys are kept inline to improve cache behavior while sorting.
 type dataSortKey struct {